What are default oracle,actual,deployed values?
Each task is solved by some candidate, so the oracle coverage is 1. Selecting candidate 0 for every task solves only task 0, so actual selection success is 0.2 (its weight), and with deployment allowed everywhere the deployed value is also 0.2. The three values are 1, 0.2 and 0.2.
Why is changed deployment 0.5 despite perfect selection?
The denied task has weight 0.5.
Can adding a candidate reduce oracle prefix coverage?
No; any previously covered task remains covered.